While bulldozers dig into slopes and developers erect structures of concrete and clay over the land, Mother Nature is constantly fighting back by moving the very soil beneath them, sometimes with disastrous results. Soil erosion is primarily caused by two of nature’s most powerful weapons: wind and water. High winds and torrential rain can bring down a mountain or open massive sinkholes, causing loss of property, buildings and occasionally, lives.
Soil erosion isn’t just a minor impediment to progress. It’s an ongoing process that requires ingenuity and determination to control.
While we may never be completely victorious in the war against Mother Nature’s wrath when it comes to soil erosion, sometimes it’s enough to win a few small battles along the way. The most effective weapons to help accomplish this are rolled erosion control products (RECPs).
RECPs are designed to be rolled over a prepared seeded surface and fastened to the soil. There are a number of different materials that RECPs are made of, ranging from straw blankets to coconut fiber to synthetic fiber held together with biodegradable netting.
Erosion control mats or blankets (ECBs) work together with a host of hydroseed partners to protect the topsoil and keep the seeds from blowing away, or washing down the slope during a rain event. Because they are made of biodegradable materials, once their job is done, they recycle themselves back into the earth, returning the landscape to its natural beauty.
Traditionally, RECPs were manufactured from a wide variety of different materials, including coconut fiber (coir), jute, straw, hay, or wood. Whether you choose a mat or a blanket will be based on the specific project’s requirements.
“What determines the type of product you’ll use will depend on the location of your construction site, the slope, the soil, and the different types of performance,” says Diane Hitt, general manager, East Coast Erosion Blankets, Bernville, Pennsylvania. “The choice really depends on a number of criteria, such as the slant of the slope, permissible shear stress, maximum flow velocity and functional longevity, to name a few.”
For instance, when a landfill in
Richmond, Georgia, needed to expand, they were required to install stormwater ponds to protect the bordering creek and wetland. The native soil onsite was composed of a highly erodible sandy clay material, so the project engineers chose a single net ECB with engineered curled and barbed excelsior fibers, manufactured by American Excelsior Company, Arlington, Texas.
“The first step to protecting the highly erodible slopes was to spread three inches of topsoil material across the surface,” said Jerry Bohannon, director of earth science division at American Excelsior. “Next, all the slopes were seeded, covered with the blankets and anchored to the soil surface with 6" wire turf staples. The vegetation grew through the excelsior matrix and successfully kept the soil on the slopes and out of the stormwater ponds.”
As a result of the growth of the vegetation, the ECBs successfully protected the erodible slopes, which kept the soil from eroding into the stormwater ponds.
This soil erosion solution, composed of seeds, fertilizer and topped with an ECB, work together effectively to keep soil in its place. But problems may arise if the intimate contact between an ECB and the soil is lost because the ECB is too dense or thick. In these cases, vegetation may struggle to penetrate the ECB, which may cause the blanket to be lifted upward. This process is sometimes referred to as product “tenting” and results in the loss of intimate contact between the product and the soil surface. It’s important to not only choose the best ECB, but the sturdiest seeds as well.
“There are varieties of grass seeds that germinate quickly and have longer root expression. We inoculate the seeds with additives that help initiate the germination and establish the vegetation quickly,” says Russ Nicholson of Pennington Seed in Madison, Georgia.
“A rye grass will germinate in one to three days, with a deep root system that will reach down two feet into the soil, so you’re able to get more moisture to the vegetation.”
Mark Doudlah, president of Agrecol Corporation, Evansville, Wisconsin, says that in some applications, a good mix of natives could help strengthen the root system even further. “Natives will establish in a period of about three weeks; the harder germinating species can take up to three months. Because of their deep root system and different types of roots, natives tend to hold up well and the mixture helps restore the landscape back to its original state.”
Unfortunately, the one drawback to applying seeds to restore a slope is that there must be soil underneath for the roots to grow. After the destruction of construction, all that will be left of graded slopes will be rough, ground-up rock. For these situations, compost erosion control blankets (CECB) come to the rescue.
CECBs first came onto the soil erosion scene around the mid-to late 1980s. They started taking off slightly in the ’90s and today they’re very much in vogue because of increased stormwater management regulations.
CECBs can be applied to any soil surface: rocky, frozen, flat, or steep. They create a permeable surface and fill in small crevices to organically promote the establishment of vegetation on the surface. Composts used in CECBs are usually made from a variety of waste products, including municipal yard trimmings, food residuals, separated municipal solid waste, biosolids and manure.
Seeds can be applied onto the blanket itself, but the more effective method is to have the seeds and compost mixed together before it’s applied to the slope. Compost blankets facilitate plant growth by capturing and retaining moisture, providing a suitable microclimate and nutrients for seed germination.
According to Rob Tyler, CEO of Filtrexx International in Grafton, Ohio, a CECB is a 1/2" to 2" deep blanket typically applied to slopes with pneumatic blower trucks or similar equipment. Once the blanket settles down, grass seed is injected into the compost. “The seed isn’t topically applied like a hydroseeder, so if there is a torrential rainstorm, or if the wind blows the seed off the top of the blanket, you still have seed in the underlying layers.”
Compost blankets can be applied by themselves, or in with other types of organic mats, such as straw or coconut. “Used together, it’s the best of both worlds,” Tyler said.
While for the most part RECPs are meant for temporary application until the vegetation is well established, turf reinforcement mats (TRMs) are designed to stay in place permanently. Like RECPs, TRMs can incorporate natural fiber materials to help establish vegetation; however, the permanent reinforcement structure of TRMs is composed entirely of high-density polypropylene non-degradable plastic.
TRMs are classified as a soft engineering practice (SEP) by the Environmental Protection Agency. SEPs lie somewhere between hard-armor erosion control techniques such as concrete blocks, rock riprap, and reinforced paving systems and Best Management Practices (BMP) classification of RECPs.
Mats were laid down on slopes to control soil erosion until revegetation occurs.
TRMs are resistant to UV-rays, so they won’t break down in the sun. They also have a thick, threedimensional netting structure that’s very difficult to wear away, compared to a normal single-net structure. Basically, TRMs are the “Superman” of mats—tougher, heavier and longer-lasting.
“TRM mats can be made of a combination of agricultural straw, coconut fiber and stabilized polypropylene, but the netting is only composed of stabilized polypropylene, which in some situations can cause problems,” says Hitt. “The nets can harm wildlife and trap animals, which is why we’re looking into new biodegradable products.”
Realizing the need to secure ECBs and protect small animals, Global Netting Solutions, Minneapolis, Minnesota, created a line of wildlife-friendly biodegradable netting with greater spacing, to lower the possibility that animals will become trapped.
“The first step to protecting highly erodible slopes is to spread topsoil, then seed and cover the area with blankets and anchor to the soil surface with wire turf staples.
The vegetation will grow through the excelsior matrix and keep the soil on the slopes and out of the stormwater ponds.”
Wanting to improve on the way netting degrades, the company launched their Ecocycle line of netting in 2007. Ecocycle uses oxo-biodegradable additives that enables the netting to lose strength at a controlled rate. Only after the netting is no longer needed to reinforce the RECP and the vegetation will it begin to lose strength, become brittle and disintegrate. As the netting ages, it becomes brittle, breaking into small fragments. The fragments break down further until they are digestible by microbes in a second stage of biodegradation.
“The Ecocycle netting works pretty much the same as standard netting,” says company Marketing Director Sean Syring. “Although the degradation process is accelerated by sunlight and elevated temperatures, UV light isn’t required.
After the intended useful life, the bottom and top layers break down through oxygen and heat, providing enhanced product life cycle performance.”
With the new advances in soil erosion control products, product testing is becoming more impor tant than ever. Organizations such as the American Society for Testing and Materials (ASTM) have industry standards that manufacturers of ECBs strive to meet or exceed.
In addition, the Erosion Control Technology Council, the Quality Data Oversight & Review Program and the National Transportation Product Evaluation Program conduct technical quality performance testing on a continuing basis.
“We’re definitely noticing how important these tests and evaluations are when it comes to the performance of ECBs. With the EPA’s stormwater and construction site runoff regulations becoming stricter, quality performance programs are essential,” says Hitt.
Progress may mean plowing through nature’s mountains to make way for man’s highways, but it can also mean that man can create eco-friendly and biodegradable soil erosion products that return to the earth some of what was taken.
It’s a battle worth fighting and one that RECPs are winning.
A perfect example of proper installation is the new growth at the pond’s edge.
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